To cause a target circuit of an exemplary system to run, a turn-on circuit powers the target circuit for an initial period of time followed by a power circuit that powers the target circuit for a secondary period of time. The turn-on circuit supplies power to the target circuit. Upon receiving sufficient power from the turn-on circuit, the target circuit supplies power to the power circuit that thereby charges an output voltage to a voltage level sufficient to power the target circuit. The turn-on circuit ceases to power the target circuit once the power circuit has charged to the voltage level sufficient to power the target circuit. Should the power circuit charge to a voltage level less than the voltage level sufficient to power the target circuit, the turn-on circuit continues to supply power to the target circuit.
In one example, the target circuit exhibits hysteresis. Hysteresis is the promotion of a delay in a change in the output voltage level of the target circuit upon a change in the input voltage level of the target circuit. The hysteresis exhibited by the target circuit in one example serves to prevent the change of the output voltage level of the target circuit upon the change in the input voltage level of the target circuit. Exemplary changes to the input voltage level of the target circuit result from a presence of a voltage rectifier and filter.
For example, the target circuit exhibiting hysteresis allows the input voltage level of the target circuit to vary between a first voltage level (e.g., 9.2 Volts (“V”)) and a second voltage level (e.g., 8.4 Volts) before a consequent change in the output voltage level of the target circuit results. The first voltage level in one example defines an input voltage level the target circuit requires to first begin to operate, for example a power-on voltage. The second voltage level in one example defines a minimum input voltage level the target circuit requires to operate. Where the input voltage of the target circuit varies between 9.2 Volts and 8.4 Volts, the hysteresis exhibited by the target circuit causes the output voltage level of the target circuit to remain consistent and further causes the target circuit to remain operational. By preceding the target circuit with a turn on circuit that switches a voltage higher than 9.2 Volts (e.g. 15 Volts), the range between the first voltage level and the second voltage level is increased.
In another example, the target circuit omitting the hysteresis responds with a change in the output voltage level of the target circuit upon a change in the input voltage level of the target circuit. For example, the target circuit comprises a voltage level (e.g., ten Volts) that defines the input voltage level the target circuit requires to operate. If the input voltage level of the target circuit drops to a voltage level less than ten Volts, the output voltage level of the target circuit changes.
In one example, the turn-on circuit comprises an active start-up circuit. The active start-up circuit provides power to the target circuit until the power circuit charges to a voltage level sufficient to power the target circuit. Where the power circuit charges to the voltage level sufficient to power the target circuit, the active start-up circuit turns off. The active start-up circuit comprises a resistor that is connected in series with a Zener diode, the combination connected in parallel with a gain-stage device.
Where the power circuit fails to charge to a voltage level sufficient to power the target circuit, the gain-stage device of the active start-up circuit draws excessive current. The current drawn by the gain-stage device of the active start-up circuit destroys the gain-stage device, preventing further use of the active start-up circuit. In order to shield the gain-stage device in the event of such a fault condition, extra circuitry is required to sense and detect the fault condition. The extra circuitry required to sense and detect the fault condition serves to provide robustness to the system in the event of such a fault condition. Yet, the addition of the extra circuitry required to provide robustness to the system in the event of such a fault condition is one shortcoming of the system.
Furthermore, where the power circuit fails to charge to a voltage level sufficient to power the target circuit, the active start-up circuit dissipates power through the current drawn through the gain-stage device. The power dissipated by the gain-stage device of the active start-up circuit in such a fault condition is another shortcoming of the system.
In another example, the turn-on circuit comprises a passive start-up circuit. The passive start-up circuit provides power to the target circuit before the power circuit charges to a voltage level sufficient to power the target circuit and after the power circuit charges to a voltage level sufficient to power the target circuit. The passive start-up circuit comprises a resistor that is connected in series with a capacitor.
Where the power circuit charges to a voltage level sufficient to power the target circuit, the passive start-up circuit does not turn off. The current drawn through the resistor in the passive start-up circuit continues to dissipate power even after the power circuit charges to the voltage level sufficient to power the target circuit. The power dissipated by the passive start-up circuit is another shortcoming of the system.
During an exemplary fault condition, the turn-on circuit responds to the fault condition by supplying power to the target circuit omitting hysteresis. The turn-on circuit in one example serves to provide power to the target circuit for a duration of time. After the duration of time in which the turn-on circuit supplies power to the target circuit, the turn-on circuit halts the supply of power to the target circuit for a duration of time. After the duration of time in which the turn-on circuit halts the supply of power to the target circuit, the turn-on circuit again supplies power to the target circuit for the duration of time. The duration of time between the turn-on circuit supplying power to the target circuit and the turn-on circuit halting the supply of power to the target circuit serves to power the target circuit at a frequency that keeps the output voltage level of the power circuit consistent. Where the power circuit remains powered during a fault condition results in power dissipation in the power circuit and over-voltage conditions on the outputs of the power circuit. The power dissipated by the power circuit is another shortcoming of the system.
The over-voltage condition in one example serves to destroy components within the power circuit, for example a rectifier and filter component. In order to shield the components of the power circuit, extra circuitry is required to sense and detect the over-voltage condition. The addition of extra circuitry to isolate components of the power circuit is another shortcoming of the system.
Thus, a need exists for a reduction in the circuitry added to the turn-on circuit to provide robustness under fault conditions. There also exists a need for a reduction in the amount of power dissipated by the turn-on circuit. There also exists a need for a reduction in the amount of power the power circuit dissipates under fault conditions. There exists a further need for a reduction in the circuitry added to the power circuit to provide robustness under fault conditions.